Land drainage has long been accomplished through underground conduits or pipes formed of tile or tubing. In recent years, the tubing has taken the form of perforated flexible corrugated drainage tubing. In connection with such land drainage, it has long been recognized that certain types of soil will quickly clog drainage lines unless provision is made for protecting the drain tile or tubing against intrusion of soil particles. Various filter materials have been proposed and have been developed for preventing such early blockage of a drainage line, including knitted fabric protective sleeves or filters known as Circular-Knit geotextile or “sock” filtration fabric.
Circular knit geotextiles are commonly used to encase perforated pipe of various types to prevent the infiltration of soil particles into the perforated pipes when used in sub-surface drainage systems. The most common type of perforated pipe onto which this product is installed is a corrugated high density polyethylene (HDPE), but the product is often applied onto perforated galvanized steel, perforated aluminum, polyvinylchloride (PVC) and ABS pipes. The pipes are produced in lengths of up to 5,000 lineal feet, depending upon the diameter of the pipe. The most common lengths of pipe are 10 feet, 25 feet, 50 feet, 100 feet and 250 feet and their metric equivalents.
The tubular-knit geotextile fabric is produced in a textile mill on circular knitting machines, collected on rolls, and is normally, but not always, supplied to the pipe manufacturers to be installed onto the pipes as the pipes are being manufactured. The length of fabric on each roll may, by coincidence, be similar to the pipe lengths, but is not normally sold or purchased in terms of lineal measure as the unit of sale is typically by weight, either pounds or kilograms. Alternatively the product is now sold in pre-measured roll or package lengths to be applied to the pipes at some later time.
The fabric is sold into two different markets, one being to manufacturers of the perforated pipe (OEM), the other to the consumer, end user or do-it-yourself via wholesale and retail outlets such as retail building supply and construction supply outlets who stock and sell the perforated pipe.
As far as the OEM market is concerned, large rolls of unspecified lengths of fabric are typically supplied to the perforated pipe manufacturer. The manufacturer then applies the fabric to the perforated tubing (typically as part of an inline process, as the tubing is being produced although it can be a secondary process). The tubing manufacturer then sells the fabric covered perforated pipe to installation contractors or to resellers of construction products, such as Home Depot, Lowe's, Ace Hardware, etc. The current practice by the pipe manufacturer is to initially transfer a length of fabric from the roll onto the outside of a cylindrical tube (commonly referred to as the application cylinder, tube or barrel). The cylinder is made of a variety of different materials such as steel, aluminum, or even PVC or ABS plastic of various length having an inside diameter of such size that a perforated pipe can pass through it. The application cylinders will vary in diameter depending upon the outside diameter of the perforated tubing to be covered and the type of material and thickness of the material from which the hollow application cylinder is made. The length of the hollow application cylinder usually is determined by (a) the physical space available within the manufacturing facility, (b) the type of materials from which the cylinder is made, and (c) the diameter of pipe and resulting fabric that is being used. The outside diameter and length of the cylinder, the maximum cross-wise stretch of the fabric and the method of application of the fabric to the cylinder dictates the maximum quantity of fabric that can be applied to the application cylinder.
The application cylinders vary in length from one manufacturer to another, but are typically 8 to 12 feet in length. By way of example, it is common to apply 2 to 3 of the rolls of fabric, each being approximately 900 feet in length, to a 12-foot long cylinder in a system applying fabric to a 4″ diameter tubing.
The procedure can be time consuming and sometimes requires extra labor on the production floor. As extrusion line speeds have increased over the years to upwards of 120 feet per minute, the manufacturer is prevented from taking advantage of the increase in production rates available to them. They must slow their extrusion speeds to match the rate at which their employees can load the geotextile product to the application cylinders which requires the extrusion line speeds to be reduced to the range of 30-60 feet per minute.
More recently, automatic pipe coiling equipment has been introduced in North America that virtually eliminates the need for downstream labor in pipe production facilities. These systems allow 4-inch tubing to be produced and coiled at speeds of over 90 feet per minute. Unfortunately, however the automatic coiling systems, as they now exist, do not yet work well with filtered tubing due to difficulties in handling and transferring the filtered tubing. Currently when filtered pipe is being made, the automatic coilers must be taken offline and manual labor put back into the line.
The fabric, once loaded onto the exterior of the application cylinder, is typically tied into a knot or closed shut at the exiting end of the application cylinder or tube. As the pipe is extruded, corrugated and perforated, it enters into the application cylinder which is now covered with the knitted fabric and exits the cylinder at the opposite end. As the perforated tubing exits the cylinder, it pushes off and carries the geotextile fabric with it. The geotextile fabric is then properly seated on the outside of the perforated tube or pipe.
When the desired length of pipe has been produced, the now covered pipe is cut at the exiting end of the application cylinder, the fabric is retied and the process is repeated. When all the fabric has been consumed from the application cylinder, the pipe is severed at the entry end of the cylinder and is typically redirected into a second cylinder which has been covered with fabric as the fabric from the first cylinder is being applied. In some installations the system has no second cylinder and therefore the cylinder must be reloaded before production of geotextile covered tubing can begin again. The lead end of the pipe is joined to the end of the previous length, the fabric from the second cylinder is pulled over the fabric on the first length of pipe to form a continuous coverage of the perforated tubing and the process continues.
The other market, known as the do-it-yourself market or the retail market is where end users purchase rolls of non-covered, perforated tubing from any one of a number of supply outlets like Home Depot, Lowe's, Ace Hardware, etc. The non-covered perforated tubing is supplied to the retail outlets by the tubing manufacturers as described above. In addition to the perforated tubing, the consumer can and sometimes will purchase a pre-measured length of fabric which is normally packaged and supplied in roll form. The consumer or do-it-yourselfer must then apply the fabric themselves to the non-covered perforated tubing. Pulling the fabric over a length of tubing is not an easy task. Currently the fabric is sold to the retail outlets in packages of wound up fabric or in pre-measured lengths of fabric as arranged between the supplier and the retail outlet.